The AF Guardian was developed as a replacement for the Navy's TBF Avenger anti-submarine search & strike aircraft. The Navy ordered Grumman Aerospace Corporation to modify the developing XTB3F-1 bomber. The new plane was to be classified as "hunter-killer" carrier based anti-submarine (ASW) aircraft. The first prototype flew on 19 December 1945. Two variants of the Guardian were produced: The AF-2S for torpedo or bombing missions and the AF-2W with the large ventral radar. Designed to work in pairs, the AF-2W "hunter" member of the team had a crew of four and was unarmed, though it could carry underwing drop tanks, and had a large radome for the APS-20 search radar mounted on the belly under the cockpit The finlets were to provide lateral stability, which was affected by the radome. The AF-2S "killer" member of the team had a crew of three and could carry up to 1,800 kilograms (4,000 pounds) of munitions, including depth charges, bombs, or a homing torpedo in the bombbay, plus 12.7 centimeter (5 inch) "high velocity air rockets (HVARs)" mounted on underwing pylons. The AF-2S mounted APS-30 targeting radar in a pod under the right wing, a searchlight in a pod under the left wing, and could also carry sonar buoys.
The Guardian was the biggest single-engine piston aircraft ever flown by the US Navy. It was driven by a P&W R-2800-48W Double Wasp radial engine, providing 2,400 horsepower to a big four-bladed propeller.
A second version of the AF-2S hunter was built beginning in 1952, featuring "magnetic anomaly detector (MAD) gear with a boom on the right side of the fuselage. This variant was designated the "AF-3S", and 40 were built. The last Guardian was rolled out in March 1953, with a total of 389 of all variants built, including the prototypes. By early 1953, Guardians began to be phased out of front line Navy squadrons in favor of the S2F-1 Tracker, a combined hunter-killer aircraft. August 31, 1955 saw the end of the last operational active Navy squadron. The Guardians had slowly been transferred to U.S. Navy Reserve squadrons and mothballed. A number of Guardians ended up in civilian hands and were apparently used as "water bombers", and some of these aircraft are now on static display in museums.